Land Use Compounds Habitat Losses under Projected Climate Change in a Threatened California Ecosystem

Abstract

Given the rapidly growing human population in mediterranean-climate systems, land use may pose a more immediate threat to biodiversity than climate change this century, yet few studies address the relative future impacts of both drivers. We assess spatial and temporal patterns of projected 21st century land use and climate change on California sage scrub (CSS), a plant association of considerable diversity and threatened status in the mediterranean-climate California Floristic Province. Using a species distribution modeling approach combined with spatially-explicit land use projections, we model habitat loss for 20 dominant shrub species under unlimited and no dispersal scenarios at two time intervals (early and late century) in two ecoregions in California (Central Coast and South Coast). Overall, projected climate change impacts were highly variable across CSS species and heavily dependent on dispersal assumptions. Projected anthropogenic land use drove greater relative habitat losses compared to projected climate change in many species. This pattern was only significant under assumptions of unlimited dispersal, however, where considerable climate-driven habitat gains offset some concurrent climate-driven habitat losses. Additionally, some of the habitat gained with projected climate change overlapped with projected land use. Most species showed potential northern habitat expansion and southern habitat contraction due to projected climate change, resulting in sharply contrasting patterns of impact between Central and South Coast Ecoregions. In the Central Coast, dispersal could play an important role moderating losses from both climate change and land use. In contrast, high geographic overlap in habitat losses driven by projected climate change and projected land use in the South Coast underscores the potential for compounding negative impacts of both drivers. Limiting habitat conversion may be a broadly beneficial strategy under climate change. We emphasize the importance of addressing both drivers in conservation and resource management planning.

Modeling direct and indirect climate change impacts on ecological networks: a case study on breeding habitat of Dutch meadow birds

“…In contrast to our expectations, land use change was primarily brought about by soil subsidence in response to the sustained management of lower water levels and hardly driven by additional effects of climate change. These findings are in concordance with Riordan and Rundel (2014), who found that projected land use change was a more important driver of habitat loss for plant species than climate change in a Californian ecosystem. Because our study focuses on the impact of climate change on local habitat quality and bird densities rather than range shifts, we did not include climate envelope modeling in our study, but restricted ourselves to habitat modeling only.…”

“…A large scale switch to bioenergy crops may lead to significant landscape changes (Gaucherel et al 2010). Although it is increasingly recognized that projections of climate change impacts on ecological network quality also should include effects of autonomous land use changes (Barbet-Massin et al 2012;Van Teeffelen et al 2012;Jongsomjit et al 2013;Riordan and Rundel 2014), land use changes driven by climate change itself are rarely taken into account (but see Bakker et al 2014). The relative impact of such indirect effects of climate change on the quality of ecological networks therefore remains largely unknown.…”

Ant communities in native sage scrub, non-native grassland, and suburban habitats in Los Angeles County, USA: conservation implications

“…Because many of the remaining SS fragments are threatened by type-conversion to non-native grasslands and/or conversion to suburban/urban habitats by future development (Cox et al 2014;Goldstein and Suding 2014;Kimball et al 2014;Riordan and Rundel 2014), understanding how such landscape transformations influence arthropod biodiversity is critical to conservation efforts at multiple scales. On a local scale, our research demonstrates that conversion of SS to non-native grassland will favor a unique subset of native ant species, while conversion to suburban habitat favors a surprisingly diverse but overwhelmingly non-native ant fauna.…”

“…The resulting development and habitat modification make Mediterranean ecosystems some of the most threatened worldwide (Sala et al 2000). This is especially true in southern California and northern Mexico, which have more than double the human population density of any other Mediterranean region (Underwood et al 2009;Riordan and Rundel 2014). Moreover, southern California's human population is disproportionately concentrated in its lowlands, 20 % of which are now urban, with much of the rest suburban, agricultural, or otherwise disturbed (Underwood et al 2009).…”

Biodiversity hotspots: A shortcut for a more complicated concept

“…Source: Modified from: Schmitt (2011 Another issue is the loss of habitat structure that generally leads to a decline in species richness and biomass. The combined impacts of climate change and land use are expected to drive unprecedented rates of environmental change and biodiversity loss (Riordan and Rundel, 2014). In particular, climate change is likely to have a large impact on biodiversity, from organisms to biomes (see Bellard et al, 2012 for a exhaustive review).…”